Nausea and vomiting are serious problems frequently observed in patients receiving a cancer chemotherapeutic agent and radiotherapy, and control of the nausea and vomiting is a very important auxiliary treatment for undergoing satisfactory treatment for cancer. Since it is reported that intravenous administration of high-dose metoclopramide is effective in inhibition of the vomiting (Gralla, R. J. et al., N. Engl. J. Med. 305, 905-909 (1981)), the vomiting has better, though not perfectly, been controlled. However, it has been revealed that presently available antiemetics, particularly compounds containing a benzamide structure, are associated with adverse reactions such as sedation, ataxia, diarrhea and tasikinesia due to their dopamine-blocking activities and central nerve-depressant activities.
Specific antagonists of 5-HT.sub.3 receptors which have recently been reported to inhibit vomiting induced during cancer chemotherapy (Cunningham, D. et al., The Lancet, 1, 1461-1463 (1987)) are considered as a potent antiemetic ones without adverse reactions associated.
Compounds having antagonists activity at 5-HT.sub.3 receptors have been described previously. For example U.S. Pat. Nos. 4,486,441; 4,563,465; 4,789,673; 4,803,199 and 4,910,207; UK Patent Specification No. 2152049A and European Patent Specification No. 0309423A2 disclose compounds containing an azabicyclic moiety structure and European Patent Specifications Nos. 0297651A1 and 0307145A1 disclose compounds containing an imidazole ring structure.
Under such circumstances it has been desired to develop selective antagonists of 5-HT at 5-HT.sub.3 receptors.